The present invention relates to a Spinal Cord Stimulation System. A spinal cord stimulation system is a programmable implantable pulse generating system used to treat chronic pain by providing electrical stimulation pulses from an electrode array placed epidurally near a patient""s spine. The present invention emphasizes the following specific features included within a spinal cord stimulation system: (1) a recharging system, (2) a system for mapping current fields, (3) optional pulse ramping control, and (4) electrode impedance measurements.
Spinal cord stimulation (SCS) is a well accepted clinical method for reducing pain in certain populations of patients. SCS systems typically include an implanted pulse generator, lead wires, and electrodes connected to the lead wires. The pulse generator generates electrical pulses that are delivered to the dorsal column fibers within the spinal cord through the electrodes which are implanted along the dura of the spinal cord. In a typical situation, the attached lead wires exit the spinal cord and are tunneled around the torso of the patient to a sub-cutaneous pocket where the pulse generator is implanted.
Spinal cord and other stimulation systems are known in the art. For example, in U.S. Pat. No. 3,646,940, there is disclosed an implantable electronic stimulator that provides timed sequenced electrical impulses to a plurality of electrodes so that only one electrode has a voltage applied to it at any given time. Thus, the electrical stimuli provided by the apparatus taught in the ""940 patent comprise sequential, or non-overlapping, stimuli.
In U.S. Pat. No. 3,724,467, an electrode implant is disclosed for the neuro-stimulation of the spinal cord. A relatively thin and flexible strip of physiologically inert plastic is provided with a plurality of electrodes formed thereon. The electrodes are connected by leads to an RF receiver, which is also implanted, and which is controlled by an external controller. The implanted RF receiver has no power storage means, and must be coupled to the external controller in order for neuro-stimulation to occur.
In U.S. Pat. No. 3,822,708, another type of electrical spinal cord stimulating device is shown. The device has five aligned electrodes which are positioned longitudinally on the spinal cord and transversely to the nerves entering the spinal cord. Current pulses applied to the electrodes are said to block sensed intractable pain, while allowing passage of other sensations. The stimulation pulses applied to the electrodes are approximately 250 microseconds in width with a repetition rate of from 5 to 200 pulses per second. A patient-operable switch allows the patient to change which electrodes are activated, i.e., which electrodes receive the current stimulus, so that the area between the activated electrodes on the spinal cord can be adjusted, as required, to better block the pain.
Other representative patents that show spinal cord stimulation systems or electrodes include U.S. Pat. Nos. 4,338,945; 4,379,462; 5,121,754; 5,417,719 and 5,501,703.
The dominant SCS products that are presently commercially available attempt to respond to three basic requirements for such systems: (1) providing multiple stimulation channels to address variable stimulation parameter requirements and multiple sites of electrical stimulation signal delivery; (2) allowing modest to high stimulation currents for those patients who need it; and (3) incorporating an internal power source with sufficient energy storage capacity to provide years of reliable service to the patient.
Unfortunately, not all of the above-described features are available in any one device. For example, one well-known device has a limited battery life at only modest current outputs, and has only a single voltage source, and hence only a single stimulation channel, which must be multiplexed in a fixed pattern to up to four electrode contacts. Another well-known device offers higher currents that can be delivered to the patient, but does not have a battery, and thus requires the patient to wear an external power source and controller. Even then, such device still has only one voltage source, and hence only a single stimulation channel, for delivery of the current stimulus to multiple electrodes through a multiplexer. Yet a third known device provides multiple channels of modest current capability, but does not have an internal power source, and thus also forces the patient to wear an external power source and controller.
It is thus seen that each of the systems, or components, disclosed or described above suffers from one or more shortcomings, e.g., no internal power storage capability, a short operating life, none or limited programming features, large physical size, the need to always wear an external power source and controller, the need to use difficult or unwieldy surgical techniques and/or tools, unreliable connections, and the like. What is clearly needed, therefore, is a spinal cord stimulation (SCS) system that is superior to existing systems by providing longer life, easier programming and more stimulating features in a smaller package without compromising reliability. Moreover, the surgical tools and interconnections used with such SCS system need to be easier and faster to manipulate. Further, the stimulating features available with the system need to be programmable using programming systems which are easy to understand and use, and which introduce novel programming methods that better address the patient""s needs.
The present invention addresses the above and other needs by providing an SCS system that is designed to be superior to existing systems. More particularly, the SCS system of the present invention provides a stimulus to a selected pair or group of a multiplicity of electrodes, e.g., 16 electrodes, grouped into multiple channels, e.g., four channels. Advantageously, each electrode is able to produce a programmable constant output current of at least 10 mA over a range of output voltages that may go as high as 16 volts. Further, in a preferred embodiment, the implant portion of the SCS system includes a rechargeable power source, e.g., a rechargeable battery, that allows the patient to go about his or her daily business unfettered by an external power source and controller. The SCS system herein described requires only an occasional recharge; the implanted portion is smaller than existing implant systems, e.g., having a rounded case with a 45 mm diameter and 10 mm thickness; the SCS system has a life of at least 10 years at typical settings; the SCS system offers a simple connection scheme for detachably connecting a lead system thereto; and the SCS system is extremely reliable.
As a feature of the invention, each of the electrodes included within the stimulus channels may not only deliver up to 12.7 mA of current over the entire range of output voltages, but also may be combined with other electrodes to deliver even more current. Additionally, the SCS system provides the ability to stimulate simultaneously on all available electrodes. That is, in operation, each electrode is grouped with at least one additional electrode. In one embodiment, such grouping is achieved by a low impedance switching matrix that allows any electrode contact or the system case (which may be used as a common, or indifferent, electrode) to be connected to any other electrode. In another embodiment, programmable output current DAC""s (digital-to-analog converters) are connected to each electrode node, so that, when enabled, any electrode node can be grouped with any other electrode node that is enabled at the same time, thereby eliminating the need for the low impedance switching matrix. This advantageous feature thus allows the clinician to provide unique electrical stimulation fields for each current channel, heretofore unavailable with other xe2x80x9cmultichannelxe2x80x9d stimulation systems (which xe2x80x9cmultichannelxe2x80x9d stimulation systems are really multiplexed single channel stimulation systems). Moreover, this feature, combined with multi-contact electrodes arranged in two or three dimensional arrays, allows xe2x80x9cvirtual electrodesxe2x80x9d to be realized, where a xe2x80x9cvirtualxe2x80x9d electrode comprises an electrode that appears to be at a certain physical location, but really is not physically located at the apparent location. Rather, the virtual electrode results from the vector combination of electrical fields from two or more electrodes that are activated simultaneously.
As an additional feature of the invention, the SCS system includes an implantable pulse generator (IPG) that is powered by a rechargeable internal battery, e.g., a rechargeable Lithium Ion battery providing an output voltage that varies from about 4.1 volts, when fully charged, to about 3.5 volts, when ready to be recharged. When charged, the patient can thus operate the IPG independent of external controllers or power sources. Further, the power source is rechargeable using non-invasive means, meaning that the IPG battery (or other power source) can be recharged by the patient as needed when depleted with minimal inconvenience. A full recharge of the rechargeable battery may occur in less than two hours. In operation, the SCS system monitors the state of charge of the internal battery of the IPG and controls the charging process. It does this by monitoring the amount of energy used by the SCS system, and hence the state of charge of the IPG battery. Then, through a suitable bidirectional telemetry link, the SCS system is able to inform the patient or clinician regarding the status of the system, including the state of charge, and makes requests to initiate an external charge process. In this manner, the acceptance of energy from the external charger may be entirely under the control of the SCS implanted system, and several layers of physical and software control may be used to ensure reliable and safe operation of the charging process. The use of such a rechargeable power source thus greatly extends the useful life of the IPG portion of the SCS system, and means once implanted, the IPG can operate for many, many years without having to be explanted.
Additionally, the SCS system of the present invention is more easily programmed and provides more stimulating features than have been available with prior art devices. The programming systems used with the invention are designed to be very user friendly, and provide novel programming methods that greatly enhance the ability of the patient, or medical personnel, to identify a pattern and location of applied stimulation that is effective for treating (minimizing or removing) pain.
The SCS system of the present invention further offers a device that is in a smaller package, without compromising reliability, than has heretofore been available. Moreover, the surgical tools and interconnections used with the SCS system are designed to be significantly easier and faster to manipulate than the tools and interconnections used with prior art systems.
All of the above and other features advantageously combine to provide an SCS system that is markedly improved over what has heretofore been available. One embodiment of the invention may be characterized as an SCS system that includes implantable components and external components. The implantable components comprise a multichannel implantable pulse generator (IPG) having a power source and an electrode array detachably connected to the IPG. The electrode array has n electrodes thereon, where n is an integer of at least eight (in a preferred embodiment, n is sixteen). The external components comprise a handheld programmer (HHP) that may be selectively placed in telecommunicative contact with the IPG, and a clinician programmer that may be selectively coupled with the HHP.
Another embodiment of the invention may be characterized as an implantable pulse generator (IPG) system for use with a spinal cord stimulation system. Such IPG system includes an implantable pulse generator and an external portable charger. The IPG comprises: (a) an hermetically sealed case; (b) electronically circuitry, including memory circuits, housed within the hermetically sealed case, wherein the electronic circuitry includes a multiplicity of independent bi-directional output current sources, and wherein each output current source is connected to an electrode node; (c) a multiplicity of coupling capacitors, wherein each coupling capacitor is connected to a respective one of the electrode nodes; (d) a header connecter attached to the sealed case, the header connecter having a multiplicity of feedthrough pins that pass therethrough, wherein each of the multiplicity of coupling capacitors is connected on the sealed side of the case to one of the feedthrough pins; (e) an electrode array having a multiplicity of electrodes thereon external to said sealed case, wherein each electrode is detachably electrically connected to one of the feedthrough pins on a nonsealed side of said sealed case, wherein each output current source generates an output stimulus current having a selected amplitude and polarity that, when the output current source is enabled, is directed to the electrode connected thereto through its respective feedthrough pin and coupling capacitor; (f) a rechargeable battery that provides operating power for the electronic circuitry; (g) a secondary coil; (h) a rectifier circuit; and (i) battery charger and protection circuitry that receives externally generated energy through the secondary coil and rectifier circuit, and uses the externally generated energy to charge the rechargeable battery. Advantageously, the rectifier circuit may be modulated between a full-wave rectifier circuit and a half-way rectifier circuit, which modulation allows the external portable charger to detect, by monitoring reflected impedance looking into the secondary coil, when the IPG battery has been fully charged.
The external portable charger of the IPG system includes: (a) a second rechargeable battery; (b) a recharging base station that recharges the second rechargeable battery from energy obtained from line ac power; (c) a primary coil; (d) a power amplifier for applying ac power derived from the second rechargeable battery to the primary coil; (e) a back telemetry receiver for monitoring the magnitude of the ac power at the primary coil as applied by the power amplifier, thereby monitoring reflected impedance associated with energy magnetically coupled through the primary coil; and (f) an alarm generator that generates an audible alarm signal in response to changes sensed in the reflected impedance monitored by the back telemetry receiver. In a preferred embodiment, the back telemetry receiver included within the external portable charger includes alignment detection circuitry that detects when the primary coil is properly aligned with the secondary coil included within the IPG for maximum power transfer; and charge complete detection circuitry that detects when the battery within the IPG is fully charged.
Yet another embodiment of the invention may be viewed as an SCS system that includes: (a) implantable components; (b) external components; and (c) surgical components. The implantable components include a multichannel implantable pulse generator (IPG) having a replenishable power source and an electrode array detachably connected to the IPG. The surgical components include tools that assist a surgeon in positioning the IPG and electrode array. Additionally, the external components include a handheld programmer (HHP) that may be selectively placed in telecommunicative contact with the IPG. Also included is a clinician programmer that may be selectively placed in telecommunicative contact with the handheld programmer. A portable charger is also provided that may be inductively coupled with the IPG in order to recharge the IPG power source.
The SCS system of the present invention may further be characterized as including the following system components, all of which cooperatively function together to effectively treat intractable chronic pain: (1) an implantable pulse generator (IPG); (2) a hand held programmer (HHP); (3) a clinician""s programming system (CP); (4) an external trial stimulator (ETS); (5) a charging station (CHR); (6) surgical tools (ST); (7) a lead extension (LEX) and an electrode array (EA); and (8) a lead anchor (LA) and suture sleeve (SS).
The implantable pulse generator (IPG) is realized using a low power pulse generator design housed in an hermetically-sealed Titanium 6-4 case. The IPG communicates with the hand held programmer (HHP) via a telemetry link. The IPG contains the necessary electronics to decode commands and provide a current stimulus to sixteen electrodes in groups of up to four channels. Features of the IPG include: (a) a rechargeable Lithium Ion battery that is used as the main power source, thereby greatly extending the life of the system compared to devices on the market, (b) user control over stimulus parameters, and (c) safety circuits and back telemetry communication to reduce risk.
The hand held programmer (HHP) comprises an external programmer that may be used by the patient or clinician to change the stimulus parameters of the IPG or external trial stimulator (ETS) via a telemetry link. The HHP thus comprises an integral part of the clinician""s programming environment. The HHP includes a belt clip or other form of convenient carrying to enable the patient to easily carry the HHP with him or her. Features of the HHP include: (a) a small size that will fit in the user""s palm with an easy to read LCD screen, (b) a software architecture that provides ease of programming and user interface, and (C) a field replaceable primary battery with sufficient energy for approximately one year of operation.
The clinician""s programming (CP) system is used to optimize the programming of the IPG or ETS for the patient. The CP system comprises a computer, an infra-red (IR) interface, and a mouse and a joystick (or equivalent directional-pointing devices). Features of the CP system include: (a) a database of the patient, (b) the ability to take stimulus threshold measurements. (c) the ability to program all features available within the IPG, and (d) directional programming of multiple electrode contacts with the electrode array(s).
The external trial stimulator (ETS) is an externally-worn pulse generator that is used for seven to ten days for evaluation purposes before implantation of the IPG. The ETS is typically applied with an adhesive patch to the skin of the patient, but may also be carried by the patient through the use of a belt clip or other form of convenient carrying pouch. Features of the ETS include: (a) usability in the operating room (OR) to test the electrode array during placement, (b) a full bi-directional communication capability with the clinician""s programming (CP) system, and (c) the ability to allow the patient or clinician to evaluate the stimulus levels.
The charging station (CHR) is comprised of two parts: (1) an IPG recharger and (2) a base unit. The IPG recharger uses magnetic coupling to restore the capacity of the implanted battery housed within the IPG. The IPG recharger is powered by a lithium ion cell. The base unit holds and IPG recharger when not being used to recharge the IPG battery and allows the lithium ion cell of the IPG recharger to regain its capacity after operation. The base unit is powered via a standard wall outlet. Features of the charging station (CHR) include: (a) allows full recharging of the IPG battery in a time of less than two hours, (b) provides a user interface to indicate that charging is successfully operating, and (c) may be recharged from any outlet using the base unit.
The surgical tools (ST) include an insertion needle, a tunneling device, a lead blank, an operating room (OR) cable, a set screw driver, and a sterile bag (to hold the ETS or HHP within the sterile field of the OR). Advantageously, the ST allows streamlined implantation of the electrode, tunneling of an intermediate leadwire from the electrode to the IPG, and the securing of the electrode position, once such position has been determined in surgery.
The lead extension (LEX) and electrode array (EA) comprises an electrode array having up to sixteen electrode contacts that may be independently activated by the IPG. The lead extension provides the connection between the IPG and the electrode array. In a preferred embodiment, up to two electrode arrays may be connected to the IPG. Features of the LEX and EA include: (a) the electrode array and lead extension provide the clinician with many options, e.g., one or two electrode arrays with only a single lead extension, (b) the lead bodies are soft and flexible to provide patient comfort, and (c) the electrode array is designed to be inserted through an insertion needle.
The lead anchor (LA) and/or suture sleeve (SS) are used after insertion of the electrode array into the spinal canal to secure and maintain the position of the electrode and prevent dislodgement due to axial loads placed upon the lead. Advantageously, the lead anchors or suture sleeves are very small and easy to implement by the surgeon, providing a reliable electrode/spinal cord relationship.
Each of the above system components of the SCS system are described in more detail below as part of the detailed description of the invention. In such description, additional emphasis is given relative to the following important features of the invention: (1) the recharging system, (2) the system used to map current fields, (3) pulse ramping control, and (4) automatic electrode impedance measurements.